Sex ratios

Sex could be determined for 609 specimens of C. galea and 115 specimens of C. caribaea. In C. galea, 74.4% were male. With 64.3%, the fraction of males in C. caribaea was lower (p = 0.030). Females were larger than males in both C. galea (χ2 = 133.9; p < 0.0001) and C. caribaea (F = 35.1; p < 0.0001). Both males and females were found on all but one host species (C. caribaea on Poritesfurcata Lamarck, 1816, on which only female specimens were found). Sex ratios within C. galea differed among snails associated with different host species (p = 0.0004; only including hosts with ≥ 5 specimens; Fig. 13a). After Bonferroni correction of p-values (n = 78) one pair remained significant: snails associated with Agaricia humilisVerrill, 1901 had a higher male to female ratio than snails associated with Colpophyllia natans (Houttuyn, 1772) (p = 0.032). Within C. caribaea, no variation in sex ratios between host species existed (p = 0.975; only including hosts with ≥ 5 specimens; Fig. 13b). Sex ratio of C. caribaea associated with alcyonaceans (66.0% male) and scleractinians (63.1% male) was similar as well (p = 0.845).

Fig. 13. Sex ratios of Coralliophila galea (a) and C. caribaea (b) associated with different host species. Host species are ranked based on the fraction of males. After Bonferroni correction for multiple pairwise comparisons, no significant differences remained in C. caribaea. Significant differences: *: p < 0.05.

Fig. 14. Mean shell length against the proportion of male snails per host species of Coralliophila galea (a) and C. caribaea (b). Regression was not significant for C. caribaea (b). In the linear regression, individual points were weighed per number of observations per host species. Number of observations is represented by the size of points. Points are coloured by host order (b), blue for Alcyonacea, red for Scleractinia.